Corneal Collagen Cross-Linking for Keratoconus and Corneal Ectasia

Corneal collagen cross-linking (CXL) is a treatment designed to decrease the progression of keratoconus, in particular, and other corneal thinning processes such as post LASIK and PRK ectasia. In addition, CXL appears to have beneficial visual and optical effects. In the CXL procedure, riboflavin (vitamin B2) is administered in conjunction with ultraviolet A (UVA 370 nm) producing a photochemical reaction in the corneal stroma with consequent mechanical stiffening of the cornea. Studies suggest that cross-linking is effective in decreasing progression of keratoconus and corneal ectasias. Maximum keratometry generally flattens by 1D to 3D 1 year after CXL. Similarly, corneal topography indices and higher-order aberrations generally improve after CXL. In addition to topography stabilization and improvement, best corrected visual acuity improves by about 1 Snellen line, on average, 1 year after CXL. After cross-linking, clinical outcomes appear to worsen at 1 month and improve between 3 and 12 months. During the wound healing course, there is a typical cross-linking-associated corneal haze, which peaks at 1 month and improves between 3 and 6 months, postoperatively. From the viewpoint of clinical decision-making, it is reasonable to consider all eyes with progressive keratoconus or corneal ectasia for cross-linking treatment; however, eyes with good visual acuity (better than 20/40) may be somewhat more susceptible to a loss of 1 Snellen line of acuity after CXL. New clinical studies are underway to investigate transepithelial and faster cross-linking procedures, as well as cross-linking as an adjunctive treatment with other procedures such as intracorneal ring segments, PRK, and microwave thermokeratoplasty (Keraflex).